Modern boat marinas provide slips for docking large numbers of watercraft, vessels or boats, as variously termed. Since most boats are equipped with modern electrical equipment and batteries, marina facilities typically include dock side electrical outlets at each slip. Electrical energy, typically 115 volt 60 Hz A.C. current, is supplied to that outlet over an onshore three wire type electrical distribution system. The electrical lines of that distribution system extend along the dock and connect to the slip outlets.
By plugging the onboard electrical distribution system into the slip's associated electrical outlet the boater makes an electrical connection to the marina's onshore electrical system. The electricity from that source is used to operate the various on-board electrical equipment, a principal one of which is the battery charger. The battery charger converts the supplied AC current to the direct current form, DC, and supplies the DC current to charge the boat's DC batteries. Using electrical power supplied from onshore avoids the need to continuously run the boat's gasoline or diesel engines or gasoline operated motor generators to generate that electricity while the boat is docked. Typically those fuel operated generators produce electricity at a lower efficiency than the electric company.
Many boats thus share the same onshore electrical distribution system. That communal use, however, has an undesirable adverse effect. Despite cautions and warnings to boat owners, among the large numbers of boats docked at the marina, one typically finds at least one boat with an onboard electrical system that is incorrectly wired, typically with incorrect neutral and ground polarities, creating a voltage difference between the boat's metal fittings and the surrounding water. Sometimes the marina's electrical outlet at an individual boat slip is incorrectly wired causing the same effect in the docked boat. As a consequence some electrical current propagates through the boats metal through-hull fittings, which are included in the boats electrical ground system, into the water, creating an undesired electrolysis current that corrodes metal parts. Adjacent boats, sharing the same onshore power system, complete the electrical circuit for this undesired current via the ground path that is included in all AC power systems, including the onshore electrical system. Since the onboard electrical equipment in the offending boat appears to the boat owner to be functioning normally, that undesired current goes unnoticed.
Salt water provides a low impedance electrical path, typically on the order of 0.6 ohms per foot. Although the magnitude of the electrolysis current is low, typically on the order of milliamps, a one milliamp current flowing through a through-hull fitting for a period of one year produces sufficient corrosion damage to the boat's fittings as may cause premature failure and require the fitting to be replaced. Expensive metal propellers are also affected in that way. The electrolysis current slowly, but surely, eats the metal parts away. Not only does the undesired electrolysis current cause damage on the offending boat responsible for the problem, damage also occurs to the adjacent boats innocently found within the path of that electrolysis current. In practice pleasure boats are often docked and left unattended for long periods, greater than the time spent at sea. It is not unusual for a sailor to return to his boat after a long absence and find the propeller inexplicably corroded away.
The problem is best solved by ensuring that the dock's electrical outlets are correctly wired and that vessel's electrical system is properly wired and modified only by trained personnel, initially, and, thereafter, for the vessel's electrical system to be checked from time to time to ensure continued compliance. In reality that solution is never achieved in practice.
Another way to avoid creating electrolysis currents under such circumstances is to simply disconnect the ground path. However that action results in an unacceptable fire and electrical shock hazard onboard the vessel. Another partial solution is to leave the vessel disconnected from the onshore source. However, most maritime vessels have built in electrically operated safety equipment, such as automatic bilge pumps. The power source for that safety equipment is the vessel's batteries, which have only a limited storage capacity. When a vessel is docked for long periods, shore power is required to maintain a level of charge in those batteries sufficient to operate that safety equipment. Simply disconnecting the vessel from shore power for long periods of time, allowing the battery to discharge, thus, produces an unacceptable safety hazard.
The present invention advantageously provides a solution to the electrolysis current problem. The electrolysis damage experienced by a boat under such circumstances is directly related to the amount of time the boat is connected to the onshore power distribution system. The present invention automatically reduces the duration in which any boat's onboard electrical system is connected to the onshore distribution system, interrupting electrolysis current paths and minimizing potential corrosion damage. The invention does so without compromising electrical fire and shock hazard prevention requirements and does so without creating a safety hazard.
A principal object of the invention, thus, is to prevent corrosion damage to a boat's through-hull fittings by eliminating or minimizing the duration of electrolysis currents created due to incorrect onboard electrical wiring.
Another object of the invention is to minimize the duration of any water borne electrolysis currents created by incorrect wiring of a boat's onboard electrical systems as might adversely affect the boatowner's boat or that of a neighbor.
A further object of the invention is to provide a power management system of simple and inexpensive structure for controlling the connection between a boat's electrical distribution system and the marina's electrical distribution system to eliminate or reduce corrosion damage to the boat's through hull fittings.
A large percentage of the electrical power consumed by a docked boat is used to trickle charge the boat's batteries and maintain them at full charge, a long established maintenance practice. Despite acceptance of that maintenance practice, some adverse consequences are posed. Battery fluids continually boil off from the battery or vaporize, leaving behind salts and minerals in the battery. Those salts and minerals eventually degrade the battery and reduce battery life. Then too, with the marina continually supplying power for this purpose to a large number of boats, substantial electrical power is consumed, which is expensive and is even thought to be wasteful. On the average, it is estimated that a docked boat using such trickle charge practice receives charging current for approximately 8,000 hours during a twelve month period.
The present invention avoids that waste of the marina's electricity. As an ancillary advantage the present invention permits the boat's on-board electrical system to connect to the on-shore system for substantially shorter periods, avoiding deleterious consequences for the battery, while allowing the battery to remain essentially fully charged. With the present invention it is estimated that battery charging may occupy as few as one-hundred hours during a twelve month period.
An ancillary object of the invention, therefore, is to extend the operational life of a vessel's battery.
The present invention provides the boat owner a way of avoiding corrosion of expensive boat fittings and the like. While the boat owners savings alone would give the marina operators little incentive to encourage boat owners to employ the present invention, the ancillary advantage, which the invention offers, allowing marina owners savings in the cost of electricity, an overhead expense, directly benefits marina operators as well.
Accordingly, another ancillary object of the invention is to reduce the marina's electrical supply costs through reduction of the electrical consumption required by docked boats.